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Title: EFFECT OF AN ALTERNATE WEED HOST, HAIRY NIGHTSHADE, SOLANUM SARRACHOIDES, ON THE BIOLOGY OF THE TWO MOST IMPORTANT POTATO LEAFROLL VIRUS (LUTEOVIRIDAE: POLEROVIRUS) VECTORS. MYZUS PERSICAE AND MACROSIPHUM EUPHORBIAE (APHIDID)

Interpretive Summary: Hairy nightshade, a common weed in potato fields, was found to be a better host for green peach and potato aphids than potato. The reproduction of aphids was further enhanced if the hairy nightshade plant was infected with potato leafroll virus (PLRV). PLRV-infected potato plants also were found to be better hosts for aphids than non-infected potato. Growers therefore should emphasize control of hairy nightshade in the field to reduce aphid populations and the subsequent transmission of PLRV and other potato viruses by aphids.

Technical Abstract:
Hairy nightshade, Solanum sarrachoides (Sendtner), is a ubiquitous weed in the potato agro-ecosystems and nonagricultural lands of southeastern Idaho and the Pacific Northwest (PNW). This weed increases the complexity of the Potato leafroll virus (PLRV) (Luteoviridae: Polervirus)-potato pathosystem by serving as aphid and virus reservoir. Field investigations revealed higher densities of green peach aphids, Myzus persicae (Sulzer) and potato aphids, Macrosiphum euphorbiae (Thomas), the two most important vectors of PLRV, on S. sarrachoides as compared with potato plants in the same field. Solanum sarrachoides sampled in these surveys also tested positive for PLRV. Viral-infections can alter the physiology of the plant hosts and the aphid performance. In order to understand better the potential effects of S. sarrachoides on the PLRV-potato-aphid pathosystem, the life histories of M. persicae and M. euphorbiae were compared on virus-free and PLRV-infected potato and S. sarrachoides. Individual nymphs of each aphid species were held in clip cages on plants from each treatment in order to monitor their development, survival and reproductive output. Nymphal survival for both aphids across plant species was higher on S. sarrachoides than on potato and within plant species was higher on PLRV-infected plants than on non-infected plants. With a few exceptions, similar patterns occurred for fecundity, reproductive periods, adult longevity and intrinsic rate of increase. The enhanced performance of aphids on S. sarrachoides and on PLRV-infected plants could alter the vector population dynamics and thus the PLRV-disease epidemiology in fields infested with this weed.